diff --git a/apps/web/src/oj/api.ts b/apps/web/src/oj/api.ts
index 7e94f07..c169948 100644
--- a/apps/web/src/oj/api.ts
+++ b/apps/web/src/oj/api.ts
@@ -41,6 +41,7 @@ import {
   type FlowchartStatistics,
   type SubmissionStatistics,
   type SubmissionLessons,
+  type RunnableLanguage,
   type SubmissionStatisticsGrid,
   type TodaySubmissionStatistics,
 } from "@oj2/contract"
@@ -242,8 +243,12 @@ export function getClassLesson(className?: string) {
 }
 
 /** 给这个班布置今天的题，空数组 = 清掉 */
-export function setClassLesson(className: string, problemDisplayIds: string[]) {
-  return api.put<null>("classroom/lesson", { className, problemDisplayIds })
+export function setClassLesson(
+  className: string,
+  problemDisplayIds: string[],
+  language: RunnableLanguage | null,
+) {
+  return api.put<null>("classroom/lesson", { className, problemDisplayIds, language })
 }
 
 /** 我的知识点地图（只有自己的，不能查别人） */
diff --git a/apps/web/src/oj/classroom/board.vue b/apps/web/src/oj/classroom/board.vue
index bda6fe9..2181afb 100644
--- a/apps/web/src/oj/classroom/board.vue
+++ b/apps/web/src/oj/classroom/board.vue
@@ -3,7 +3,9 @@ import { getClassBoard, setClassLesson } from "oj/api"
 import { useHiddenStudents } from "shared/composables/hiddenStudents"
 import { useCollabStore } from "shared/store/collab"
 import { useConfigStore } from "shared/store/config"
+import type { RunnableLanguage } from "@oj2/contract"
 import { errorMessage } from "utils/api"
+import { LANGUAGE_SHOW_VALUE } from "utils/constants"
 import { parseTime } from "utils/functions"
 import type { ClassBoard, ClassBoardCell, ClassBoardStudent } from "utils/types"
 
@@ -34,6 +36,16 @@ const updatedAt = ref<Date | null>(null)
 const projector = ref(false)
 
 const lessonInput = ref("")
+/**
+ * 这份作业用什么语言做，跟着这一次布置走（用户定的：不是给班级定死的设置）。默认是这个班
+ * 上一次布置时选的；选了之后看板和学生那边的「做完」都只认这个语言交对的
+ */
+const lessonLanguage = ref<RunnableLanguage>("Python")
+const LESSON_LANGUAGES: RunnableLanguage[] = ["Python", "C", "C++"]
+const languageOptions = LESSON_LANGUAGES.map((value) => ({
+  label: LANGUAGE_SHOW_VALUE[value],
+  value,
+}))
 const saving = ref(false)
 
 function classLabel(name: string) {
@@ -65,7 +77,7 @@ async function load() {
   }
 }
 
-// 换了班要把输入框换成那个班今天布置的题
+// 换了班要把输入框换成那个班今天布置的题、布置时选的语言（15 秒一次的刷新不动它们）
 watch(
   () => [board.value?.className, board.value?.source] as const,
   () => {
@@ -73,6 +85,7 @@ watch(
       board.value?.source === "teacher"
         ? board.value.problems.map((problem) => problem.problemDisplayId).join(" ")
         : ""
+    lessonLanguage.value = board.value?.language ?? board.value?.lastLanguage ?? "Python"
   },
 )
 
@@ -86,8 +99,12 @@ async function saveLesson() {
   const ids = lessonInput.value.split(/[\s,，、;；]+/).filter(Boolean)
   saving.value = true
   try {
-    await setClassLesson(className.value, ids)
-    message.success(ids.length ? "已布置，学生首页会显示这几道题" : "已清掉，学生那边改回自动推断")
+    await setClassLesson(className.value, ids, ids.length ? lessonLanguage.value : null)
+    message.success(
+      ids.length
+        ? `已布置（${LANGUAGE_SHOW_VALUE[lessonLanguage.value]}），学生首页会显示这几道题`
+        : "已清掉，学生那边改回自动推断",
+    )
     await load()
   } catch (error) {
     message.error(errorMessage(error))
@@ -241,7 +258,12 @@ function submissionsHref(
       username: student.username,
       exactUsername: "1",
       today: "1",
-      ...(flowchart ? { language: "Flowchart" } : {}),
+      // 布置时选了语言的，代码那边只看这个语言交的（和格子里数的一致）
+      ...(flowchart
+        ? { language: "Flowchart" }
+        : board.value?.language
+          ? { language: board.value.language }
+          : {}),
       ...(problemDisplayId ? { problem: problemDisplayId } : {}),
     },
   }).href
@@ -293,6 +315,12 @@ function submissionsHref(
       <n-card v-if="!projector" size="small" class="section">
         <n-flex align="center" :wrap="false">
           <n-text strong style="flex-shrink: 0">这节课的题</n-text>
+          <n-select
+            v-model:value="lessonLanguage"
+            :options="languageOptions"
+            aria-label="用什么语言做"
+            style="width: 110px; flex-shrink: 0"
+          />
           <n-input
             v-model:value="lessonInput"
             placeholder="输入题号，用空格隔开，比如 8019 8020 8021"
@@ -303,13 +331,15 @@ function submissionsHref(
         </n-flex>
         <n-text depth="3" class="meta">
           <template v-if="board.source === 'teacher'">
-            学生首页的「班里在做」显示的就是这几道。清空再点布置就改回自动推断。
+            学生首页的「班里在做」显示的就是这几道<template v-if="board.language"
+              >，用 {{ LANGUAGE_SHOW_VALUE[board.language] }} 交对才算做完</template
+            >。清空再点布置就改回自动推断。
           </template>
           <template v-else-if="board.source === 'inferred'">
             还没布置。下面这几道是按今天的提交记录推断的（同班 5 人以上做过的题）。
           </template>
           <template v-else>
-            布置之后，学生打开首页就能看到这几道题，没听清题号的也能找到。
+            布置之后，学生打开首页就能看到这几道题，没听清题号的也能找到；打开题目时编辑器默认就是左边选的语言。
           </template>
         </n-text>
       </n-card>
diff --git a/apps/web/src/oj/home/dashboard.vue b/apps/web/src/oj/home/dashboard.vue
index d3be22c..08fed85 100644
--- a/apps/web/src/oj/home/dashboard.vue
+++ b/apps/web/src/oj/home/dashboard.vue
@@ -17,7 +17,7 @@ import { useBreakpoints } from "shared/composables/breakpoints"
 import { useProblemJump } from "shared/composables/problemJump"
 import { pickHeadline, type Headline } from "oj/user/knowledge"
 import { useUserStore } from "shared/store/user"
-import { ContestStatus, CONTEST_STATUS, JUDGE_STATUS } from "utils/constants"
+import { ContestStatus, CONTEST_STATUS, JUDGE_STATUS, LANGUAGE_SHOW_VALUE } from "utils/constants"
 import { duration, parseTime, zonedParts, zonedYear } from "utils/functions"
 import type {
   AnnouncementListItem,
@@ -227,7 +227,10 @@ const classActivityTitle = computed(() => {
   const day = classActivity.value?.day
   if (!day) return ""
   // 老师在课堂看板布置的，说成「老师布置的」，比「班里在做」更让人知道该做这几道
-  if (classActivity.value?.source === "teacher") return "今天老师布置的题"
+  if (classActivity.value?.source === "teacher") {
+    const language = classActivity.value.language
+    return `今天老师布置的题${language ? ` · 用${LANGUAGE_SHOW_VALUE[language]}做` : ""}`
+  }
   if (classToday.value) return "今天班里在做"
   const [, month, date] = day.split("-").map(Number)
   return `${month}月${date}日班里做了`
diff --git a/apps/web/src/oj/problem/components/ContextBar.vue b/apps/web/src/oj/problem/components/ContextBar.vue
index fdf989f..e4ec07a 100644
--- a/apps/web/src/oj/problem/components/ContextBar.vue
+++ b/apps/web/src/oj/problem/components/ContextBar.vue
@@ -232,7 +232,10 @@ onSolvedHere(() => {
 <template>
   <!-- 课堂 -->
   <div v-if="lesson" class="context-bar lesson">
-    <span class="lead lesson-lead">这节课 做完 {{ lesson.done }}/{{ lesson.total }}</span>
+    <span class="lead lesson-lead"
+      >这节课<template v-if="lessonStore.languageText"> · {{ lessonStore.languageText }}</template>
+      做完 {{ lesson.done }}/{{ lesson.total }}</span
+    >
     <!-- 手机上放不下一排题号：只说是第几道，箭头做大（设计稿「手机：题目 / 代码 / 结果」） -->
     <span v-if="isMobile" class="meta">这是第 {{ lesson.position }} 道</span>
     <ProblemChips v-else :items="lesson.chips" :current="currentId" variant="lesson" />
diff --git a/apps/web/src/oj/problem/components/ProblemEditor.vue b/apps/web/src/oj/problem/components/ProblemEditor.vue
index 3849541..29c2ea8 100644
--- a/apps/web/src/oj/problem/components/ProblemEditor.vue
+++ b/apps/web/src/oj/problem/components/ProblemEditor.vue
@@ -16,6 +16,7 @@ import { useCollabHere, useTeacherCollab } from "../composables/teacherCollab"
 import { useProblemPageContext } from "../composables/problemPageContext"
 import CollabBar from "./CollabBar.vue"
 import { useFlowchartStore } from "oj/store/flowchart"
+import { useLessonStore } from "oj/store/lesson"
 
 const FlowchartEditor = defineAsyncComponent(
   () => import("shared/components/FlowchartEditor/index.vue"),
@@ -151,6 +152,30 @@ watch(
   },
 )
 
+/**
+ * 老师在课堂看板布置这节课时选了语言：打开这节课的题，编辑器默认就用它。学 C 的班，
+ * 编辑器停在默认的 Python（或者上一个用这台电脑的人留下的偏好）的话，学生交上去才发现
+ * 不算数。课堂条只在题库入口出现，这里同一个范围。
+ *
+ * 每道题只自动换一次：学生自己再切回别的语言，就按他的来。课堂状态可能比题面晚到
+ * （课堂条进页面才去拉），所以两边都等到了再判断；画着流程图时不动他。
+ */
+const lessonStore = useLessonStore()
+let lessonLanguageFor: string | null = null
+watch(
+  () => [problem.value?._id, lessonStore.activity] as const,
+  ([id, activity]) => {
+    if (!id || !activity || lessonLanguageFor === id) return
+    lessonLanguageFor = id
+    const language = activity.language
+    if (!language || ctx.value.entry !== "problem" || teacherCollab.value) return
+    if (!lessonStore.includes(id) || !problemStore.codeLanguages.includes(language)) return
+    if (codeStore.code.language === language || codeStore.code.language === "Flowchart") return
+    problemStore.switchLanguage(language)
+  },
+  { immediate: true },
+)
+
 /**
  * 画着流程图时忽然不让画了：工具栏的「写代码 / 画流程图」和语言下拉都跟着 canDraw 藏起来，
  * 编辑器要是还停在画布上，学生就回不去写代码了。拖窄到手机宽度时页面会换一套布局、编辑器
diff --git a/apps/web/src/oj/store/lesson.ts b/apps/web/src/oj/store/lesson.ts
index 04233fa..b220e97 100644
--- a/apps/web/src/oj/store/lesson.ts
+++ b/apps/web/src/oj/store/lesson.ts
@@ -1,5 +1,6 @@
 import { defineStore } from "pinia"
 import { getClassActivity } from "oj/api"
+import { LANGUAGE_SHOW_VALUE } from "utils/constants"
 import type { ClassActivity, ClassActivityProblem } from "utils/types"
 
 /** 同一节课里来回换题不用每次都重拉；过了这么久再进题目页就重拉一次 */
@@ -74,10 +75,18 @@ export const useLessonStore = defineStore("lesson", () => {
     return { total: list.length, next: rest[0] ?? null, remaining: rest.length }
   }
 
-  /** 老师布置的叫「老师布置的题」，推断出来的叫「这节课的题」 */
+  /** 老师布置时选的语言，给界面写「C语言」；没选（推断出来的课、以前布置的）为空 */
+  const languageText = computed(() => {
+    const language = activity.value?.language
+    return language ? LANGUAGE_SHOW_VALUE[language] : ""
+  })
+
+  /** 老师布置的叫「老师布置的题」（选了语言带上语言），推断出来的叫「这节课的题」 */
   const label = computed(() =>
-    activity.value?.source === "teacher" ? "老师布置的题" : "这节课的题",
+    activity.value?.source === "teacher"
+      ? `老师布置的题${languageText.value ? ` · ${languageText.value}` : ""}`
+      : "这节课的题",
   )
 
-  return { activity, label, load, markAccepted, includes, nextAfter }
+  return { activity, label, languageText, load, markAccepted, includes, nextAfter }
 })
diff --git a/apps/web/src/oj/submission/list.vue b/apps/web/src/oj/submission/list.vue
index 1dea402..21e05f2 100644
--- a/apps/web/src/oj/submission/list.vue
+++ b/apps/web/src/oj/submission/list.vue
@@ -508,6 +508,8 @@ async function toggleLesson() {
   if (lessonActive.value) {
     query.problem = ""
     query.today = "0"
+    // 「这节课」顺带筛上的语言一起放掉；老师自己另选的别动
+    if (lesson.value?.language && query.language === lesson.value.language) query.language = ""
     return
   }
   lessonLoading.value = true
@@ -525,6 +527,8 @@ async function toggleLesson() {
     lesson.value = res
     query.problem = lessonIds.value
     query.today = "1"
+    // 老师布置时选了语言：看板上只数这个语言交的，列表也只列它（流程图那边不动）
+    if (res.language && !flowMode.value) query.language = res.language
   } finally {
     lessonLoading.value = false
   }